The present invention relates generally to guiding a web of moving material and more particularly to a system and method for determining the position of a web of moving material.
Many different types of materials including fabric, paper, films, foils, and the like are formed into what is commonly known as a web. In the production, processing, or treatment of a web, the web is often moving as it progresses from one operation, such as cutting, slitting, printing, and the like, to the next operation. It is important to be able to accurately determine the position of the web as it moves so that it can be properly aligned for the various operations. One commonly known technique for determining the position of a moving web involves detecting the position of the physical edge of the web using an edge detector. This is commonly referred to as edge guiding. Edge detectors typically include an optical or ultrasonic transmitter, which is placed on one side of the web, and a corresponding detector, which is placed on the opposite side of the web, that are used to detect the physical edge of the web. One such edge detector is described in U.S. Pat. No. 5,834,877 to Buisker et al.
Another technique for determining the position of a web involves detecting the position of a line appearing on the surface web. This is commonly known as line guiding. One method of line guiding involves using a light source to project light onto a surface of the web and using two photocells to receive light that is reflected off the surface. The amount of light received by each of the photocells can be compared to determine the position of the line on the surface of the web. In order for such a system to accurately determine the position of the line, there must be some appreciable contrast between the line and the background on both sides of the line that can be measured by the photocells.
However, in order to generate the necessary contrast, a light other than a white light may be required. For example, depending upon the relationship between the line and the associated background, other colors of light (i.e., light having a certain wavelength) may be required to achieve the necessary contrast. Also, if the web is made from film or other material that is sensitive to visible light, an infrared light source can be used to achieve the same results. Current line guiding systems do not allow different colored light to be projected as needed to effectively guide materials having different characteristics.
In addition, the position of the light source with respect to the light detector may vary depending upon the reflective properties of the web material. For example, if the web material has good reflective properties, as is the case with glossy or shiny metallic materials, the light source can be positioned in one location to achieve effective guiding. However, if the material has poor reflective materials, as is the case with paper or other materials having a matte finish, the light source can be placed in a different position in order to have effective guiding. Likewise, to achieve effective guiding from a material that has different reflective properties, such as holographic material, the light source can be placed in a third position. Current guiding systems to not provide the flexibility of light source configurations needed to effectively guide materials having different characteristics.
A system and method for guiding a web of moving material that overcome these deficiencies are needed.